Why won't my husband go down on me?

All sex is sometimes giving and sometimes receiving. Since humans have no sex organs in our mouths, the benefit for the giver is in the knowledge that they are making their partner feel good. It's a way of expressing how you feel about them. I'm not suggesting that he doesn't care, he may think it's not a big deal to you. If it is though, it then becomes a communication problem. Tell him how you feel about it and his answer may tell you more about how he feels about you than how he feels about oral sex.